Modern aircraft landing gear typically comprise a main shock strut having one end pivotally attached to a portion of the airplane for swinging movement of the landing gear between a retracted and extended position. The landing gear also includes a truck beam that is pivotally attached to the other end of the main shock strut, having a plurality of wheels rotatably attached thereon. It is desirable for the truck beam to be pivotally attached to the main shock strut to permit the beam to pivot and absorb the energy associated with traversing a runway discontinuity, as well as permitting the truck beam to be positioned for stowage within the airplane.
This pivotal joint along with other landing gear mechanical members are manually lubricated at a plurality of critical sites in accordance with published maintenance schedules. These schedules generally designate the frequency of such lubricative maintenance, the amount of lubricant to be applied, and the noted sites of application. A failure to perform scheduled maintenance can accelerate wear depending on the operation of the aircraft. In situations where an aircraft is operated in non-normal service, such as those aircraft operating on the rough runways characteristic of Eastern Europe, more frequent lubricative maintenance is needed.
Aircrafts operating on rough runways experience more aggressive landing gear tress. Premature pivot joint failure can be caused by the heat generated by high frequency truck beam pivoting that is characteristic of rough runway operation. Inspection of failed pivot joints has indicated that the frictional heating adversely affects the metallurgical properties of the associated assemblies causing them to become hard, brittle and susceptible to crack formation leading to ultimate failure.
Airplane operators have responded with more frequent lubricative maintenance. However, the additional time required to perform the procedure contributes unfavorably to aircraft productivity. Further, it has been observed that the relubrication of the highly loaded pivot joints typical of an airplane being supported by the extended landing gear is ineffective. In this orientation, the pivot joint bearings are loaded primarily through less than their full bearing circumference. This results in the unloaded portion of the bearing defining a gap 24, through which new lubricants have been found to take the path of least resistance, leaving the loaded portions deficient of lubrication.
For the foregoing reasons there is a need for an aircraft landing gear autolubrication system that performs periodic lubrication to a plurality of critical sites, without impact to aircraft productivity, and one that can be retrofitted easily to aircraft. The present invention is directed to a method and system that satisfies these needs. According to one aspect of the invention, a method for automatically lubricating an aircraft landing gear is provided. The method includes providing a lubricant supply distribution system for dispensing a lubricant; sensing aircraft landing gear parameters indicative of the landing gear""s extended or retracted positional state; providing a timer to control the duration of the lubrication cycle; measuring intervals of time for the duration of the lubrication cycle, and delivering lubricant from the supply distribution system to lubrication points after determining that the landing gear has experienced a retracted to extended transition, for the duration of a predetermined time interval.
According to a second aspect of the present invention, yet another method and apparatus for automatically lubricating an aircraft landing gear is provided. The method includes providing a lubricant supply system for dispensing a lubricant; providing an actuator on the landing gear such that a first end of the actuator that will move relative to and in response to the pivotal movement of the landing gear truck beam; activating the second end of the actuator through movement of the first, and delivering lubricant from the lubricant supply distribution system to one or more selected sites in response to activation of the second end.
According to a third embodiment of the present invention, an electromechanical system for automatically lubricating an aircraft landing gear is provided. The system includes a lubricant reservoir; a lubricant pump; a lubricant distribution system that fluidly connects the reservoir to the pump inlet and the pump outlet to at least one desired lubrication point; a means for producing a lubrication signal in response to sensed landing gear position parameters; a lubrication cycle timer for controlling the duration of the lubrication cycle; and a means for activating the pump in response to the lubrication signal for the duration of a predetermined time interval.
According to a fourth embodiment of the present invention, yet another electromechanical system for automatically lubricating an aircraft landing gear is provided. The system includes a lubricant supply distribution system for dispensing a lubricant to lubrication critical points; an aircraft landing gear position sensor for indicating the landing gear extended or retracted state; a lubrication cycle timer for controlling the duration of the lubrication cycle; and a control circuit for activating the lubricant supply distribution system in response to determining that the landing gear has experienced a retracted to extended transition, for the duration of a predetermined time interval.
According to a fifth embodiment of the present invention, a mechanical system for automatically lubricating an aircraft landing gear is provided. The system includes an actuator associated with the landing gear assembly wherein the actuator that moves relative to and in response to the pivotal movement of the landing gear truck beam, a pump coupled to the actuator, the pump mechanism operable for pumping in response to movement of the actuator relative to a portion of the truck beam; a lubricant supply distribution system coupled to the pump for supplying lubrication to selected locations in response to pump activation.
The present invention provides significant technical advantages including some of the following: A technical advantage of the present invention is that lubrication is automatically performed minimizing unfavorable impacts to aircraft productivity. A second technical advantage of the present invention is that the lubrication is applied to unloaded critical sites, thereby maximizing the lubricant penetration into the normally highly loaded portion of the bearings. A third technical advantage of the present invention is that the invention is easily retrofittable onto aircraft. Yet, a further technical advantage of the present invention is that the lubrication cycle is not continuous. Another feature according to an embodiment of the present invention is that electrical power is not necessarily required. Still a further technical advantage of the present invention is that the reservoir is easily filled and has the ability to self purge air out of and bootstrap the rest of the system.